/*
 * binbit.c  - 使用位操作显示二进制
 */

#include <stdio.h>
#include <limits.h> // 担任 CHAR_BIT的定位， CHAR_BIt表示每字节的位数
char * itobs(int , char *);

void show_bstr(const char *);

int main(void)
{
    char bin_str[CHAR_BIT * sizeof(int) + 1];
    int number;
    puts("Enter integers and see them in binary.");
    puts("Non-numeric input terminates program . ");
    while (scanf("%d", &number) == 1) {
        itobs(number, bin_str);
        printf("%d is ", number);
        show_bstr(bin_str);
        putchar('\n');
    }
    puts("Bye!");

    return 0;
}

char * itobs(int n, char * ps)
{
    int i;
    const static int size = CHAR_BIT * sizeof(int);
    for (i = size-1; i >=0; i--,n >>= 1) {
        ps[i] = (01 & n) + '0'; 
    }
    ps[size] = '\n';

    return ps;
}

void show_bstr( const char * str)
{
    int i = 0;
    while (str[i]) {
        putchar(str[i]); 
        if (++i %4 == 0 && str[i]) {
            putchar(' ');
        }
    }

}
